Unit 24 Quiz Flashcards
When replacing a TXV, what are three key identifying features you should look for?
The amount of revolutions/turns the original is adjusted to
The diameter dimensions of the original TXV
orientation/positioning of original TXV
The diaphragm in the TXV responds to three different pressures which act at the proper time to open, close or modulate the valve needle between open and closed. What are those three pressures?
Evaporator pressure, sensing bulb pressure, spring pressure
Charged with a fluid different from the system fluid.
Cross liquid
Instructions or programs stored in the microprocessor.
Algorithms
Contains a small amount of liquid refrigerant. Sometimes called a “critical charge” bulb. Also referred to as a maximum operating pressure valve.
Vapor charge bulb
Controls refrigerant flow by pressure drop. Calibrated by length and inside diameter.
Capillary tube
Metering valve that uses a thermistor as a temperature sensing element that varies the voltage to a heat motor operated valve.
Electronic expansion valve
Used to maintain constant pressure in the evaporator. Will starve refrigerant when suction pressure rises.
Automatic expansion valve
Difference between the superheat set point of the controller and the actual superheat.
Error/offset
Small storage tank located between the condenser and expansion device. Stores excess refrigerant during different load conditions and when servicing the system.
Refrigerant receiver
Communication between sensor and controller to open or close the valve.
Feedback loops
Used when an evaporator has a very long circuit or multiple circuits and a pressure drop occurs between the expansion valve outlet and the evaporator inlet.
External equalizer
What are the four types of sensing bulb charges?
Liquid, vapor, cross liquid, cross vapor
Superheat spring pressure is 10.4 psig, sensing bulb pressure is 51.2 psig and the evaporator pressure is 35.1 psig. Will the TXV open, close or remain in equilibrium?
Open
What type of sensing bulb charge is also known as a “critical charge” bulb?
The vapor (Gas) charge bulb
The best position for mounting a TXV sensing bulb on tubing less the 3/4” diameter is ______.
12 o’clock position
True or false: If the TXV valve body, that uses a vapor charged sensing bulb, becomes colder than the sensing bulb, the sensing bulb may not operate because the vapor in the sensing bulb has condensed and migrated to the colder valve body.
True
True or false: A balanced port TXV can be readily identified by its external equalizer tube.
False
True or false: An automatic expansion valve’s (AXV) sensing bulb must be mounted at the 5 o’clock position on the suction line at the exit of the evaporator.
False
True or false: Do not use plastic zip ties to secure the sensing bulb in place.
True